1. Fields of the Invention
The present invention relates to a motor control apparatus for an injection molding machine, which includes a control function section for stopping a drive motor for moving a movable member upon reception of a signal indicating that a safety door is opened.
2. Description of the Related Art
Conventionally, there has been known a mold clamping apparatus provided in an injection molding machine, in which a movable platen is moved by means of a servomotor (drive motor), as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 60 (1985)-112417.
FIGS. 3 and 4 show a typical mold clamping apparatus U1 utilizing a servomotor. A motor-driven injection molding machine M is composed of the mold clamping apparatus U1 and an injection apparatus U2, only the tip end portion of which is illustrated by an imaginary line.
The mold clamping apparatus U1 includes a stationary platen 32 fixed onto a machine base 31, and a drive platen 33 fixed onto the machine base 31 at a position apart from the stationary platen 32. Four tie bars 34 are disposed between the stationary platen 32 and the drive platen 33, and a movable platen 2m is slidably supported by the tie bars 34. A stationary mold 35 is attached to the stationary platen 32, while a movable mold 36 is attached to the movable platen 2m. The stationary mold 35 and the movable mold 36 constitute a molding mold.
A servo motor 3c is attached to a side surface of the drive platen 33, and a screw shaft 37s constituting a ball-screw mechanism 37 is rotatably disposed at the center of the drive platen 33. The servomotor 3c and the screw shaft 37s are connected together via a rotation transmission mechanism 38. In this case, the rotational transmission mechanism 38 is composed of a pulley 39 attached to the shaft of the servomotor 3c, a pulley 40 attached to the screw shaft 37s, and an endless belt 41 disposed between the pulleys 39 and 40 to loop around them. A nut member 37n in screw engagement with the screw shaft 37s, the movable platen 2m, and the drive platen 33 are coupled together via a toggle mechanism 42. The servomotor 3c is equipped with a rotary encoder 15c for detecting the rotational position of the servomotor 3c.
By virtue of the above-described structure, when the servomotor 3c is operated, rotation of the servomotor 3c is transmitted to the screw shaft 37s of the ball-screw mechanism 37 via the rotation transmission mechanism 38, and thus the nut member 37n advances and retracts in the axial direction of the screw shaft 37s. The advancing/retracting movement of the screw shaft 37s is transmitted to the movable platen 2m via the toggle mechanism 42, so that the movable platen 2m advances and retracts with respect to the stationary platen 32 in order to open and close the mold.
Further, the mold clamping apparatus U1 is equipped with a molding product ejection apparatus E1. As shown in FIG. 3, in the molding product ejection apparatus E1, a servomotor 3p is attached to a side surface of the movable platen 2m, and a screw shaft 51s constituting a ball-screw mechanism 51 is rotatably disposed within the movable platen 2m. The servomotor 3p and the screw shaft 51s are connected together via a rotation transmission mechanism 52. In this case, the rotational transmission mechanism 52 is composed of a pulley 53 attached to the shaft of the servomotor 3p, a pulley 54 attached to the screw shaft 51s, and an endless belt 55 disposed between the pulleys 53 and 54 to loop around them. Further, a guide rail 56 is attached to the movable platen 2m in parallel to the screw shaft 51s. One lateral end of a pin support plate 57 is slidably supported by the guide rail 56, and the other lateral end of the pin support plate 57 is fixed to a nut member 51n in screw engagement with the screw shaft 51s. A drive pin 58 which projects forward is fixed to the pin support plate 57. The servomotor 3p is equipped with a rotary encoder 15p for detecting the rotational position of the servomotor 3p.
Moreover, as shown in FIG. 5, an ejector pin unit 61 is accommodated within an internal space 36i of a movable mold 36. The ejector pin unit 61 includes a pair of ejector pins 2p and 2q fixed to a base 60. The ejector pin unit 61 is movable over a predetermined stroke in the advancement/retraction direction of the movable platen 2m. The ejector pins 2p and 2q have tip ends facing a mold cavity 62 and are urged by means of return springs 63 and 64 in the direction opposite to the ejection direction. Symbol 65 denotes a through hole for the drive pin 58, and symbol W denotes a molding product.
The mold clamping apparatus U1 having the above-described molding product ejection apparatus E1 has a safety apparatus E2. The safety apparatus E2 is equipped with a motor control apparatus 70 shown in FIG. 3. The motor control apparatus 70 has a control function section for stopping the servomotors 3p and 3c in response to an open signal So output from a limit switch 71, which detects that a safety door D is opened.
When the motor control apparatus 70 receives an open signal So indicating the opened state of the safety door D, the motor control apparatus 70 turns off the servo-on circuit (see symbol 17 in FIG. 1) built into the motor control apparatus 70, or opens an on/off switch (see symbol 12 in FIG. 1) disposed in the power line for the servomotors 3p and 3c, in order to stop the supply of electricity to the servomotors 3p and 3c.
The above-described conventional motor control apparatus 70 has the following drawbacks.
First, when the return springs 63 and 64 are provided as in the molding product ejection apparatus E1, the ejector pins 2p and 2q are pushed out against the urging force of the return springs 63 and 64. Therefore, even when the servo control for the servomotor 3p is turned off, or the power supply for the servomotor 3p is stopped, the shaft of the servomotor 3p rotates due to the urging force of the return spring 63 and 64, with the result that the ejector pins 2p and 2q are pushed back to the initial position. Therefore, the above-described operation is insufficient in terms of securing safety through a quick stop of movement.
Second, for adjusting work or monitoring work, it is necessary to stop the ejector pins 2p and 2q at a desired position and to perform adjustment and confirmation of the state at that position. However, since the ejector pins 2p and 2q and other members return to their initial positions whenever the safety door D is opened, the adjustment work and the monitoring work cannot be performed properly, resulting in increased difficulty of work and operation.